Control valves are used in a wide range of processes. Control valves may open and close proportionally and vary the degree of travel depending on the applied control signal. Valve positioners may be incorporated into a control valve that help ensure that the valve is at a desired position of opening or “travel” for the applied control signal. Processes that use control valves may be negatively impacted by a faulty or malfunctioning control valve or valve positioner.
Performing diagnostics or testing on control valves and valve positioners may require removal of the valve from the process, which can cause process delays or require a process shutdown. Some valve devices have a travel indicator that allows a technician to visually observe an amount of travel when in operation. Some valve positioners can output a position of the valve as feedback in response to an applied control signal. A set of valve positions and the corresponding control signals is known as a “valve signature.” A graphical representation of the valve signature can be useful in assessing various characteristics of a valve. Collecting valve signature data using currently available technology can be a time consuming process requiring several different test tools.
Moreover, interpreting a valve signature can require extensive training and experience in valve signature analysis. A highly-trained, experienced technician may have difficulty diagnosing a valve using a valve signature because a valve signature may vary depending on the application and process parameters such as flow, pressure, temperature, and valve settings, among others. This problem is further compounded due to various different types of valves being used in industry, and each valve may have a unique valve signature. A graphical representation of a valve signature having a particular shape may reflect a malfunction for one valve and a functional valve for another. In addition, some valves and valve positioners that simply need to be recalibrated appear to be malfunctioning, leading to an unnecessary replacement.
In view of the above, there exists a need for improved systems and methods for obtaining and using a valve signature to test a valve.